This invention relates to processes and a systems for recovering oil from oil bearing soil such as oil shales and tar sands. In particular, it relates to recovering of such oil by processes that include contacting oil bearing soil with liquid mediums.
The world population, especially in the industrial countries, consumes enormous amounts of energy. For example, in 1978 an equivalent of about 13.4 billion barrels of fuel oil was consumed in the United States alone. About half of the amount of energy was actually supplied by petroleum products. As the traditional sources of oil are being exhausted in industrial countries and as the price of the oil continues to be at a relatively high level, there is a growing need for the development of alternate sources of oil.
A virtually inexhaustible source of oil is oil bearing soil such as oil shale and tar sands. Oil recovered from oil shale and tar sands by conventional processes, such as retorting, is not identical in composition to the conventional crude oil recovered from the ground and for many applications such oil has to be further treated by distillation, coking of residue and/or hydrogenation to achieve the required composition. As used herein "oil" means organic materials including primarily hydrocarbons recovered from the ground, and the term is meant to include conventional crude, processed oil as well as oil recovered from soil even if the composition, impurities and the API number of such oil are different from the conventional crude or from the conventional processed oil.
The deposits of both tar sands and oil shale have been found on all of the inhabited continents. Although at present the precise amounts of oil available in these deposits cannot be determined, it is estimated that they would yield some 2 quadrillion barrels of oil. The United States has large shale deposits in several regions. The deposits in the Green River formation in Colorado, Utah and Wyoming are of particular interest because they contain oil shale having the highest oil concentration of any oil shale in the world. One of the largest known deposits of tar sands extends for several thousand square miles in the Athabasca District of Alberta, Canada. Large oil shale or tar sand deposits have also been found in Australia, Brazil, Bulgaria, Burma, Congo, France, Germany, Great Britain, Italy, Israel, New Zealand, South Africa, Spain, Sweden, Switzerland, Thailand, U.S.S.R. and Yugoslavia.
Despite the fact that enormous amounts of oil are present in the oil shale and tar sand deposits and the fact that such deposits are located in many of the most technologically advanced countries (including the United States and Canada), the amounts of oil actually obtained from these deposits are insignificant in the total energy picture. The reason for is that oil is trapped in the oil shale and tar sands and is extremely difficult and expensive to recover. Specifically, in the oil shale, the organic fraction (called kerogen) is composed of carbon and hydrogen molecules cross-linked together by sulfur and oxygen atoms to form macromolecules with molecular weights of about 3000. These macromolecules are embedded within a matrix of inorganic or mineral materials. The problem in recovering oil from oil shale is that it is extremely difficult to separate kerogen from the inorganic matrix. Kerogen is insoluble in most standard petroleum solvents and has to be heated to relatively high temperatures in order to effect a separation. At a temperature of about 204.degree. C. (400.degree. F.) chemical bonds between and within the organic molecules break down and the smaller molecules formed as a result can be separated as a liquid or gaseous product from the inorganic matrix.
It is also difficult to separate and recover oil from tar sands because organic material is bound to and between interstices of sand. Thus, heat or special solvents are required to break the organic material away from the sand.
Most of the commercial operations for recovering oil from shale or tar sands have used the heating (retorting) method for separating the oil. In fact, the recovery of oil by heating oil shale or tar sands goes back some 150 years. The efforts to improve on the basic method have been expanded in a number of countries, spurred by the oil embargo and the significant rise in the price of oil. Despite the use of the finest technical talents and the expenditure of enormous amounts of money by giant industrial corporations, these efforts have been unsuccessful in devising a commercially successful process which can be used to make oil shale a significant contributor of world's energy requirements. Some of the retorting processes, developed thus far, are described in a report entitled "An Assessment Of Oil Shale Technology" published by The Congress of the United States, Office of Technology (1980), and in an article appearing in Chemical Engineering, September 7, 1981, pages 47-51, and 63-71. The magnitude of the efforts that went into the unsuccessful development of a commercially feasible and profitable process and system is illustrated by the withdrawal of Exxon Company, U.S.A. from the oil shale venture after spending millions of dollars.
The reason for the failures of the retorting processes is that they use enormous amounts of energy, require huge capital expenditures and produce by-products--spent shale or sand--which have to be treated in order to support vegetation. More specifically, enormous amounts of energy must be used to heat large amounts of oil bearing soil to the required retorting temperatures which generally range between about 500.degree. C. (900.degree. F.) and about 800.degree. C. (1500.degree. F.). Large capital expenditures are needed for building the equipment to effect heating of the oil bearing soil, even if the heating is done in situ. The spent (or processed) soil subjected to a retorting process generally has an alkaline pH. Processed shales retorted at temperatures of about 500.degree. C. (900.degree. F.) generally have pHs ranging from about 8 to 9 and those retorted at temperatures of 750.degree. C. to 800.degree. C. (1400.degree. to 1500.degree. F.) have pHs of 11 or 12. In order to use such spent shales as growth media for plants, their alkalinity must be reduced. The pH reductions can be achieved by adding acids or acid-formers to the shale; however, such treatment significantly raises the overall costs of the recovery process. Additionally, the spent shales have high concentrations of boron, molybdenum, selenium, arsenic and Fluorine which can be toxic to animals which feed on plants grown in such soil. The retorting processes also result in relatively low yields--30 to 40%--in part because heating shales to above about 500.degree. C. transforms some of the organic materials into char.
Another approach to recovering oil from oil bearing soil including shale and tar sands has been to extract oil from oil bearing soil with solvents. For example, U.S. Pat. No. 4,242,195 (Rudnick) discloses extraction of organic constituents, such as hydrocarbons and phenols from tar sands and oil shales. The Rudnick patent discloses extraction using a solvent predominantly comprising certain organic sulfoxides, organic sulfones, or mixtures thereof. U.K. Patent No. 1,495,722 (Williams, et al.) discloses extracting oil from oil shale using a variety of organic solvents at elevated temperatures (80.degree. C. to 550.degree. C.) and at elevated pressures (500 to 10,000 psi). Recently, McKay et al. have proposed a process for recovery of organic components of oil shale which involves penetrating the shale with a methanol-water solution and then extracting the organic material by refluxing it with a benzene/methanol mixture. This experimental process is conducted at about 400.degree. C. See "Nonretorting Method Recovers Shale Organics," Chemical & Engineering News September 14, 1981.
The proposed extraction processes have not been entirely successful because they employ organic solvents which are generally quite expensive. Additionally, many of the processes also require, for commercial production, high temperatures and high pressures. The use of high temperatures and/or pressures, in turn, necessitates sophisticated and expensive equipment.
There is, therefore, a long felt and unsatisfied need for a commercially viable process and system for recovering oil from oil bearing soil including oil shale and tar sands, which process does not suffer from the aforementioned disadvantages.
Thus, one object of the present invention is to provide a process for recovering oil from oil bearing soil including oil shale and tar sands, which is inexpensive and creates minimal pollution and disposal problems.
Another object of this invention is to provide a process for extracting oil from oil bearing soil including oil shale and tar sands that requires small capital expenditures and significantly less energy to operate than the retorting processes.
A further object of the present invention is to provide a process for recovering oil from oil bearing soil, such as oil shale or tar sands that does not require high temperatures and pressures for its operation.
Still another object of the present invention is to provide a process and a system for recovering oil from oil bearing soil, such as oil shale or tar sands, which utilizes a liquid medium that is inexpensive.
A still further object of the present invention is to provide a process for recovering oil from oil bearing soil, such as oil shale or tar sand, using a liquid medium which can be recycled.
Still another object of the present invention is to provide a process for the recovery of oil from oil bearing soil such as oil shale and tar sands, which produces a spent soil that does not impair vegetation and has a pH value close to neutral.
A still further object of the present invention is to provide a process for the recovery of oil from oil bearing soil, such as oil shale or tar sands, which uses an inexpensive and easily available medium composed primarily of water.
Still another object of the present invention is to provide a high-yield process for recovering oil from oil bearing soil such as oil shale or tar sands.
Other objects of the invention will become apparent to those skilled in the art upon studying this disclosure.